1. Field of the Invention
This invention relates to a semiconductor laser module with a built-in optical isolator which will be suitable as a transmission light source for optical communication.
2. Description of the Prior Art
Conventional semiconductor laser modules with a built-in optical isolator can be classified into the following two technical groups. In the first technical group, the beam incidence surface of a Faraday rotator consists of a convex surface in order to prevent reflection from the Faraday rotator as described, for example, in JP-A-63-182617. The second technical group employs the structure wherein a lens for condensing the beams passing through an optical isolator and coupling them optically to an optical fiber is fixed after its position is adjusted to the optical isolator passing beams and the optical fiber is then fixed to the lens after its position is adjusted. The technique of this kind is described in JP-A-63-252497.
However, the first conventional technique described above does not take into consideration the fact that when an LPE (Liquid Phase Epitaxy) thick film grown by liquid phase epitaxy is used for the Faraday rotator and the size of this Faraday rotator is reduced in the direction of thickness, machining of the convex surface necessary for preventing reflection becomes impossible. Therefore, it involves the problem that reflection from the optical isolator itself cannot be reduced.
In accordance with the second conventional technique described above, the coupling lens must be first adjusted and fixed to the optical isolator and the optical fiber must then be adjusted and fixed to the coupling lens. In other words, this technique does not much consider the reduction of man-hours for assembly and the reduction of the number of positions requiring adjustment and fixing and involves the problems such as the increase in a machining cost and the increase in fluctuation factors of coupling efficiency due to position errors of adjustment-fixing portions.